It is well known that so-called "chamber" gas meters contain at least one deformable membrane which separates two adjacent displacement measuring chambers. The gas whose flowrate is to measured is injected into and evacuated from the measuring chambers and causes the membrane to move back and forth. Membrane motion is transmitted by a mechanical system to a counter which thus serves to display the quantity of gas which has passed through the measuring chambers. The periphery of the membrane is fixed to the common wall of the chambers and the central portion of the membrane is fixed to the mechanism which connects the membrane to the counter.
In order for the gas meter to supply the desired measuring accuracy, it is necessary for the membrane itself to have well-specified properities. It must be gastight to a very high degree. For example, the membrane must be able to withstand a pressure of 50 millibars for a period of one minute with practically no leakage. The membrane must also be very flexible and it must be able to withstand mechanical fatigue as tested by endurance tests. For example, the membrane must be capable of withstanding 2,000,000 cycles at a frequency of 100 cycles per minute without suffering significant deterioration. Further, the membrane must not suffer from exposure to the various hydrocarbons which may be present in the gas to be measured. In particular, the tests require a membrane to withstand a mixture of toluene and heptane.
Traditionally, this type of meter has made use of membranes made from specially selected and treated goatskin. They are relatively expensive. Because of the above-mentioned requirements, it has long remained difficult to make membranes out of synthetic material which have the desired characteristics. Thus proposals have already been made to make the membrane from a structure of woven fibers, e.g. polyester fibers with the structure being impregnated with layers of synthetic rubber. Such rubber-impregnated structures present storage problems by virtue of self-vulcanization phenomena which occur over time at ambient temperature. This solution suffers from the drawback that the synthetic rubber must be vulcanized in order to acquire its final properties. Such vulcanization consumes non-negligible quantities of energy. Further, as is well known, synthetic rubber processing gives rise to non-negligible pollution risks.
Proposals have also been made to provide membranes using a single layer of plastic material. None of these attempts has yet given results which are satisfactory for use in a gas meter.
In order to remedy these drawbacks, an aim of the invention is to provide a method of making membranes which are usable in gas meters and which do not require vulcanization techniques, while nevertheless enabling membranes to be obtained whose mechanical strength and flexibility are sufficient, while still remaining chemically inert relative to materials likely to be present in the gas to be measured.